The present invention is related to analog to digital conversion, and more particularly to systems and methods for reducing kickback in relation to analog to digital conversion.
Turning to FIG. 1, an analog to digital conversion system 100 including a Delta-Sigma Modulator is shown. Analog to digital conversion system 100 includes two integrators 110, 120, two summation elements 150, 160, a digital to analog converter 140, and an analog to digital converter 130. An input signal (u) and a feedback signal from digital to analog converter 140 are aggregated by summation element 150. The aggregate from summation element 150 is applied to integrator 110. The output of integrator 110 is aggregated with the feedback signal from digital to analog converter 140 using summation element 160. The aggregate from summation element 160 is applied to integrator 120, and the output of integrator 120 is applied to analog to digital converter 130. The output (v) of analog to digital converter 130 is a digital representation of the aforementioned input signal (u), and is provided to digital to analog converter 140 to create the previously discussed feedback.
Analog to digital conversion system 100 is typically used in low bandwidth applications such as digital telephony and digital audio which rely on high oversampling ratios to achieve the desired signal to noise ratio and linear performance. In contrast, analog to digital conversion system 100 does not work well at low oversampling ratios (i.e., oversampling ratios less than eight to sixteen) due primarily to non-linearities caused by variations in manufacturing processes and circuit imperfections. In some cases, analog to digital conversion system 100 has been implemented with high quality analog components to address some of the causes of the aforementioned non-linearities, however, even with the use of such high quality components analog to digital conversion system 100 is generally not capable of adequate operation at low oversampling rates (i.e., eight to sixteen or less).
Turning to FIG. 2, another analog to digital conversion system 200 including a Delta-Sigma Modulator is shown. Analog to digital conversion system 200 has been proposed to address some of the limitations of analog to digital conversion system 100. Similar to analog to digital conversion system 100, analog to digital conversion system 200 includes two integrators 210, 220, a digital to analog converter 240, and an analog to digital converter 230. Three summation elements 250, 260, 270 are also included. An input signal (u) and a feedback signal from digital to analog converter 240 are aggregated by summation element 250. The result of the aggregation is the difference between the input signal (u) and the output signal (v), or the error (e). The aggregate from summation element 250 is applied to integrator 210. The output of integrator 210 is applied to integrator 220. The output of integrator 220 is applied to summation element 260. In addition, the output of integrator 210 is fed forward via an amplifier 280 to summation element 260. The output from summation element 260 is summed with the input signal (u) in summation element 270, and the output of summation element 270 is applied to analog to digital converter 230. The output (v) of analog to digital converter 230 is a digital representation of the aforementioned input signal (u), and is provided to digital to analog converter 240 to create the previously discussed feedback.
While analog to digital conversion system 200 substantially alleviates the previously discussed linearities of analog to digital conversion system 100, it has not found much use in high bandwidth implementations. This is because the circuit has a tendency to be very noisy at or near the band of interest. The level of noise seems to be less when the circuit is used at relatively high oversampling rates (i.e., eight to sixteen or greater), but renders the circuit unreliable at lower oversampling rates.
Thus, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for analog to digital conversion.